1. Field of the Invention
Generally, the present invention relates to an outsole of shoes. More particularly, the present invention relates to an outsole having high gripping force to obtain superior slip prevention performance even on ground irregular and wet so that the outsole can be used safely and suitably for trekking shoes.
2. Description of the Related Art
The slip prevention performance of shoes is an important capability thereof. Thus, the outsole which is a part of the shoes and contacts the ground is formed of a rubber composition to provide the shoes with slip prevention performance by an adhesive frictional force peculiar to rubber.
When the ground is dry, the outsole formed of the rubber composition has a superior slip prevention performance. But when the ground is wet, for example, on a rainy day or the waterside and the like, the degree of its slip prevention performance deteriorates. Therefore, it is necessary to limit a person""s exercise range or the person may turn over in the worst case. This is because when the ground is wet, a water film is present between the outer surface of the outsole and the ground, thus deteriorating the adhesive frictional force therebetween.
To allow the outsole to have slip prevention performance on the wet ground, proposals have been made to form the outsole of a rubber composition containing a material having a high water absorbing percentage so that the outsole absorbs the water present between the outer surface of the outsole and the ground. However, according to the proposal, there is a limitation in the amount of water which can be absorbed by the outsole; and sucked water increases the weight of the shoes, which makes it difficult for the person to walk or take exercise.
Instead of using the material having a high water absorbing percentage, as disclosed in Japanese Patent Application Laid-Open No. 9-322806, there is proposed an outsole made of a rubber composition containing a material having a low water absorbing percentage, namely, 0 wt % or more and 1 wt % or less. The outsole is intended to discharge water present between the outer surface of the outsole and the wet ground to the periphery thereof to a possible highest extent to thereby prevent the outsole from slipping on the wet ground. Although the console is formed of the rubber composition having a low water absorption percentage, the outsole is incapable of providing a satisfactory degree of slip prevention performance for shoes such as trekking shoes used to walk on very irregular ground such as a rocky place when the irregular ground is wet.
As apparent from the above description, it is difficult to provide the outsole to be used for the irregular and wet ground with a high slip prevention performance by means of control of the water absorbing property of the rubber composition composing the outsole. Therefore, it is necessary to enhance the slip prevention performance of the outsole.
The present invention has been made in view of the above-described situation. Thus, it is an object of the present invention to provide an outsole having preferable slip prevention performance by improving the ground-gripping performance thereof even for ground very irregular and wet.
In the present invention, an outsole of shoes is comprising molded vulcanized rubber material which contains base rubber. The base rubber contains 70-100 wt % of styrene-butadiene rubber whose glass transition temperature (Tg) is higher than xe2x88x9233xc2x0 C. and less than xe2x88x9210xc2x0 C.